Conventionally, so-called active matrix driving has been employed, and the active matrix driving is such that: thin film transistors (hereinbelow referred to as TFT) such as a-Si (amorphous Si) and p-Si (polycrystalline Si) are formed on a glass substrate, so as to drive a liquid crystal display panel, an organic EL panel, and the like. Further, by using the p-Si whose mobility is so high as to operate at a high speed, peripheral drivers have been integrated. Alternately, study has been performed with respect to forming of a device which utilizes higher-performance Si so as to integrate a system constituted of an image processor, a timing controller, and the like, that are required to have higher performance.
This is because the polycrystalline Si brings about the following problems: because of (a) a localized state in the band gap that is caused by incomplete crystallization, (b) deficiency in the vicinity of a crystal grain boundary, drop in the mobility that is caused by the presence of the localized state in the band gap, and (d) increase in an S coefficient (sub-threshold coefficient), performance of the transistor is too insufficient to form a high-performance device of Si.
Then, in order to form a higher-performance device of Si, not only laser crystallization, but also the following techniques have been proposed: a technique for improving crystallization, for example, further advanced techniques such as SLS (Sequential Lateral Solidification) and the like (for example, a specification of U.S. Pat. No. 6,300,175 (Publication date: Oct. 9, 2001), CLC (CW Laser Lateral Crystallization)(for example, A. Hara et al., “Ultra-high Performance Poly-Si TFTs on a Glass by a Stable Scanning CW Laser Lateral Crystallization”, 2001 International Workshop on Active Matrix Liquid Crystal Displays—TFT Technologies and Related Materials—(AM-LCD2001), Digest of Technical Papers, p. 227-230, Jul. 11-13, 2001, Japan Society of Applied Physics). These techniques are to deposit an a-Si film on a glass substrate so as to control the crystallization in a preferable manner, or so as to realize single crystallization.
However, in these techniques using laser, a merely Si film is heated to a high temperature so as to perform crystal growth while keeping a temperature of an insulating substrate whose heat resistance is low like glass etc. Thus, generally, a tensile stress of approximately 109 Pa is exerted on the Si film, so that there occur such problems: cracks appear in the film, reproducibility in the TFT property is deteriorated, non-uniformity is large, and the like.
While, there is a technique in which the single crystal Si is bonded to the insulating substrate so as to make the film thinner (for example, Japanese Laid-Open Patent Application No. 211128/1993 (Tokukaihei 5-211128)(Publication date: Aug. 20, 1993). With this technique, it is possible to form an oxide film on the single crystal Si substrate, and to form the single crystal Si thin film thereon. However, when the single crystal Si thin film is to be bonded to an insulating substrate other than the Si substrate, for example, a glass substrate or a quartz substrate, there occurs such problem that Si is stripped because of a thermal-expansion-coefficient difference between Si and the insulating substrate such as the quartz substrate.
In order to prevent the foregoing damage brought about in the thermal-bond-strength-improving process due to the thermal-expansion-coefficient difference between Si and the quartz substrate, there is proposed a method of changing composition of crystallized glass (for example, Japanese Laid-Open Patent Application No. 163363/1999 (Tokukaihei 11-63363) (Publication date: Jun. 18, 1999).
Further, as described above, conventionally, there have been brought about dramatic improvements in (a) an integrated circuit element technique such that: the single crystal silicon substrate is processed and hundreds of millions of transistors are formed on the substrate, and (b) a thin film transistor (TFT) liquid crystal display technique such that: after a polycrystal semiconductor thin film such as a silicon film is formed on an amorphous material such as a glass substrate, they are processed into a transistor, so as to make picture elements and drivers of a liquid crystal display, as well as popularization of computers and personal information terminals using liquid crystal displays.
In these techniques, the integrated circuit element is made by processing a commercial single crystal silicon wafer whose thickness is scant 1 mm and diameter ranges from 150 mm to 300 mm, and forming a large number of transistors on the processed single crystal silicon wafer. Further, in the TFT liquid crystal display, an amorphous silicon film on an amorphous nonalkali glass is fused/polycrystallized by heat of laser etc., and the amorphous silicon film is processed, so as to form a MOS type transistor which functions as a switching element.
In fields of the liquid crystal display and the organic EL display using the TFT, a TFT of an amorphous silicon film or a polysilicon film is formed on a transparent glass substrate, so as to form a device of silicon for driving the picture element, that is, for performing so-called active matrix driving. Further, in order to integrate the peripheral drivers, the timing controller, and the like as a system in terms of the active matrix driving, forming of a higher-performance device of silicon has been studied. This is because the polycrystalline Silicon film brings about the following problem: because of (a) a localized state in the band gap that is caused by incomplete crystal, (b) drop in the mobility, or (c) increase in a sub-threshold coefficient (S coefficient) that are brought about by the presence of the localized state in the band gap in the vicinity of a crystal grain boundary, performance of the transistor is too insufficient to form a high-performance device of silicon.
Then, attention is paid to an SOI technique. The SOI is the abbreviation of Silicon on Insulator, and is a technique for forming a single crystal semiconductor thin film on an insulating substrate (this technique is seldom used to form a polycrystalline Silicon film). The technique has been actively studied since around 1981. Further, the SOI substrate used in the field of the integrated circuit is to dramatically improve performance of the semiconductor element by using preferable transistors. Thus, as long as the substrate functions as an insulating film, it does not matter whether the substrate is transparent or not, or it does not matter whether the substrate is crystalline or amorphous. In this field, when the transistor is formed by using the SOI substrate, elements are completely separated, so that there is little restriction in operating, thereby obtaining preferable property as a transistor.
Now, as a representative of the SOI substrate, a SIMOX (Separation by Implantation of Oxygen) substrate is on sale. In the SOI substrate, oxygen is implanted into a silicon wafer, and the thus formed silicon oxide layer separates a single crystal silicon thin film from a bulk of the substrate. Thus, oxygen which is an element much heavier than hydrogen is implanted to a predetermined depth so that the implantation is performed at high energy and at high dose. Thus, crystals are severely damaged, so that there occur the following problems: it is impossible to obtain sufficient property of the single crystal, or it is impossible to obtain complete insulating property because of deviation from stoichiometry of a silicon dioxide film portion.
Then, Tokukaihei 5-211128 discloses a technique such that: the single crystal silicon is bonded to the substrate, and this is made to be a thin film. This prior art is called “smart cut process”, and is such that: hydrogen ions are implanted into a single crystal silicon substrate in accordance with an ion implantation process, and the resultant is bonded to an enforcing member, and minute bubbles are brought about in a hydrogen ion implanted layer by a heating process, and the single crystal silicon substrate is divided at the hydrogen ion implanted layer, so as to form the single crystal silicon thin film, so that the SOI structure is realized. As a result, it is possible to manufacture a single crystal silicon transistor whose element property is high. From this view point, the technique is superior.
However, as to this prior art, Tokukaihei 5-211128 discloses merely that: the oxide film is formed on the single crystal silicon substrate, and the single crystal silicon thin film is formed thereon. The suitability for other substrates such as the glass substrate for display is not taken into consideration. Then, Tokukaihei 11-163363 mentions examples in which other substrates are compared in terms of the bonding suitability. In the prior art, it is recited that: crystallized glass is used to prevent the damages of the substrate in the heating process for improving the bond strength with respect to the substrate, and composition thereof is changed so as to correspond to the silicon piece in terms of the thermal expansion rate.
However, the crystallized glass typically contains alkali atoms, and has property contrary to a transistor whose property is stabilized. Further, in the foregoing techniques, the single crystal Si substrate is shaped in a wafer of 6, 8, and 12 inches in diameter, so that the insulating substrate which is to be bonded is limited to a substrate of 6, 8, and 12 inches. Thus, it is impossible to manufacture large size liquid crystal display panel and organic EL panel. In a case of a small size panel, the manufacturing cost becomes high, and it is difficult to use the technique in practice.
Moreover, in a case of using a quartz substrate, when the single crystal Si substrate is bonded to the insulating substrate, the bond strength drops because of the thermal expansion rate difference. Further, in a case where a stress is exerted on a bonded interface, the TFT property is deteriorated because of differences and non-uniformity in the stress exerted on the interface.
Further, in the prior art, it is considered that: when the single crystal silicon substrate is bonded, it is impossible to obtain the sufficient bond strength unless exposed in a high temperature. Thus, a temperature for performing the heating process is 800° C. to 1200° C. It is considered that a high-heat-resistant crystallized glass whose strain point is not less than 750° C. is suitable, so that there occurs the following problem: the technique cannot be applied to a high-strain-point nonalkali glass, typically used in a liquid crystal panel of the active matrix driving, whose strain point is not more than 700° C.